I think the parent actually agrees with you and so do I. Art has value in and of itself in that it conveys an emotion, idea, or context. It can also have value through artistry; how difficult it was to create or how novel it is. That value exists whether the work is one of one or whether it is one of two hundred million. A collectible meanwhile does not have much inherent value (like the hat) and derives most of its value from being rare. If it wasn't rare, it would be substantially less valuable and potentially irrelevant. As you point out, those things are not mutually exclusive and you can certainly have art that is also a collectible.